Sunglasses are often used when riding on motorcycles, driving convertibles or playing outdoor sports such as skiing. Sunglasses protect the eyes not only from ultraviolet rays but also from being hit directly by airflow during high-speed moving.
There is another option available, in the form of goggles. The frame or lenses of goggles have their perimeters completely enclosed by a wall that prevents wind and dirt from coming in, there is no airflow coming into the space enclosed by the lenses and the frame. This prevents wind and airflow from affecting the eyes.
Human eyes are constantly lubricated with tears supplied by lachrymal glands. Lachrymal glands are located above and laterally outward of respective eyeballs, i.e. above respective lateral angles of eyes. Therefore, tears flow above the lateral angles of eyes toward the medial angles of eyes, lubricating and protecting the eyes from various stimuli.
Now, when moving forward at a high speed, with the face oriented ahead, the face is hit by a flow of air. The airflow is divided by the nose ridge in right and left directions, and then continues to flow along the face. When eyeglasses are worn, the airflow along the face comes into gaps between the eyeglasses and the face, and flows over the eyeball surfaces in directions against the flow of tears. This interferes the flow of tears, and dries the eyes even if eyeglasses are worn. Also, this often causes inflammation in the eyes. For this reason, conventional sunglasses and eyeglasses often do not work as a windshield when riding on motorcycles, skiing, and so on.
In an attempt to alleviate the problem, some eyeglasses are designed so that the lenses and the frame will be closer to the face. However, placing the lenses and the frame simply closer to the face does not eliminate the gap between the face and the lenses. Therefore, this does not prevent the airflow along the face from coming sideways behind the eyeglasses. Further, if the lenses are placed too close to the face, lens surfaces make contact with user's cilia, and are often smudged or otherwise damaged.
Goggles, which have surrounding walls capable of sealing entirely around the eyes, can perfectly prevent the airflow along the face from entering the inner space behind the eyeglasses. However, due to the surrounding wall design, the user's face looks so different that there is resistance in people to wearing goggles in the same manner as they wear eyeglasses in their daily lives. Further, due to the need for the surrounding wall to be fitted to the contours of the face, goggles must be constantly pressed against the face by means of a rubber band for example. For this reason, it is troublesome to wear goggles. Still further, it is difficult to incorporate nicely looking outer design in goggles. In addition, the lenses of goggles, which are isolated from the outer atmosphere, will easily be clouded when there is a temperature difference between inside and outside of the goggles, often making it difficult to see clearly and widely enough.
Sometimes, ordinary eyeglasses mounted with prescription lenses are converted to sunglasses by providing color coating on the prescription lenses or by attaching a colored plate over the prescription lenses for shielding ultraviolet rays.
However, the colored plate is placed over the outer surface of the lenses. This interferes with originally designed looks, and reduces the esthetic value of the eyeglasses. Further, the colored plate, which is detachable from the lens outer surface, does not have a very firm hold in place, and therefore can be vibrated by strong airflow or potentially blown off the eyeglass frame.